Engine Control System

DIAGNOSTIC CHART

Diagnostic Chart:

Diagnosis
Abnormal air flow sensor signal.
Harness connector between ECM and air flow sensor is shorted or open.

Trouble Symptom
Engine stalls, poor idling, poor driveability.

CHECK INPUT SIGNAL FOR ECM

Input Signal:

1. Turn ignition ON.
2. Measure voltage between ECM and body.

Connector & Terminal Voltage
(E30) 5 - body 0 - 0.3 V
(E31) 1 - body 0 V

3. Start engine and let idle.
4. Measure voltage between ECM and body with engine at idle.

Connector & Terminal Voltage
(E30) 5 - body 0.8 - 1.2 V
(E31) 1 - body 0 V

CHECK POWER SUPPLY TO MASS AIR FLOW SENSOR

Power Supply Test:

1. Turn ignition OFF.
2. Unplug connector from air flow sensor.
3. Turn ignition ON.
4. Measure voltage between air flow sensor connector and body.

Connector & Terminal Voltage
(E25) 1 - body 10 - 13 V

CHECK HARNESS CONNECTOR BETWEEN ECM AND AIR FLOW SENSOR

Harness Test:

1. Turn ignition OFF.
2. Unplug ECM connector.
3. Measure resistance of harness connector between ECM and air flow sensor.

Connector & Terminal Resistance
(E30) 5 - (E25) 2 10 ohms max.
(E30) 22 - (E25) 3 10 ohms max.
(E30) 3 - body 10 ohms max.

Harness Test:

4. Measure resistance of harness connector between EDM and body to ensure no short.

Connector & Terminal Resistance
(E30) 5 - body 1 M ohms min.
(E31) 1 - body 1 M ohms min.